1. Field of the Invention
This invention relates to the repair and connection of downhole casing in a wellbore, and more particularly, to a tool system and method for repairing damaged areas, closing gaps between casing sections and filling other openings in well casing by flame spraying, plasma spraying, welding and other similar methods.
2. Description of the Prior Art
When well casing is installed in a wellbore, there may be gaps formed between casing joints. This is a particular problem, for example, between a lateral casing and the wall to which it is welded. Such gaps can be from several inches to as much as twenty feet or more. Closing this gap is a very difficult and time-consuming operation. This is also true in repairing a large damaged area or filling other openings in casing.
Filling such gaps or damaged areas using wire feeder type welding apparatus, either electric or laser type welders, may in fact prove to be impossible. In such cases, the problems associated with such openings may require different operations in the well, and in extreme cases may mean abandonment of that particular wellbore and the drilling of a new well. Obviously, this is a very undesirable situation, and there is thus a need for equipment and techniques to fill gaps or make repairs quickly and easily within the casing in the wellbore.
The present invention solves this problem by providing an apparatus and method for using techniques such as flame spray or plasma spray technology to do the job. It is estimated with this apparatus that about one-half pound per minute of metal may be deposited to the desired area in the casing, so even large areas can be repaired quickly. Unlike standard above-ground welding techniques, flame spraying or plasma spraying allow the metal to be applied directly to the bare wellbore and not just to the metal of the casing. In this way, the thickness of the deposited layer of metal can be built up as needed and spread out to adjacent casing surfaces. Like welding, the filled area becomes an integral part of the adjacent casing section or sections.
The present invention provides methods and apparatus for downhole welding to repair downhole casing in a wellbore and/or to close other openings in the casing or between sections of casing. This is accomplished by flame spraying, plasma spraying, welding, or other techniques for applying metallic material.
Thus, the invention may be described as a method of closing an opening in a wellbore casing string comprising the step of filling the opening with metallic material while the casing string is positioned in the wellbore. The opening in the wellbore casing string may be a damaged area of the casing string, a gap formed at adjacent ends of a pair of casing sections, or any other opening in the casing string.
A preferred embodiment of the apparatus comprises an oxygen supply such as a tank, a fuel tank, a metal supply, and metal depositing means in communication with the oxygen tank, fuel tank and metal supply such that heat is generated by the mixture of oxygen and fuel, and heated metal is deposited in the opening of the well casing and adhered thereto.
The fuel tank is filled with a fuel preferably from the group consisting of liquefied petroleum gas, kerosene and acetylene. The liquefied petroleum gas may include, for example, butane or propane.
The apparatus may comprise meters for metering flow of oxygen from the oxygen tank and fuel from the fuel tank. When the fuel is kerosene, the flow of oxygen is preferably less than about 280 standard cubic feet per gallon of kerosene.
The apparatus may additionally comprise a camera and a light disposed adjacent to the camera for lighting an area toward which the camera is directed. The operator may use the camera to guide the spray head to a desired area in the casing. This guiding of the spray head may be carried out by a steering sub adapted for connection to a tool string whereby the spray head may be rotated and reciprocated within the casing so that the spray head may be directed to the desired area in the casing.
In a preferred embodiment, the metal supply is a quantity of metal powder, and the metal depositing means comprises a powder container in which the metal powder is disposed. The metal depositing means further comprises a spray head in communication with the oxygen tank, fuel tank and powder container such that the mixture is a mixture of oxygen, fuel and metal powder which is discharged as a metallized flame spray from the spray head.
In this flame spray embodiment, the apparatus preferably further comprises an inert gas tank in communication with the powder container. The inert gas tank is filled with an inert gas which pushes the metal powder into the spray head. The inert gas is preferably selected from the group consisting of nitrogen and argon. The inert gas is also mixed with the mixture of oxygen, fuel and powder in order to boost flame speed of the flame discharged from the spray head.
In an alternate embodiment, rather than oxygen, a tank may be filled with a gas such as nitrous oxide (N2O) and decomposed into oxygen and nitrogen by adding heat, such as by a sparking device. The decomposition reaction creates additional heat which continues the reaction thus providing oxygen for combustion of the fuel and nitrogen as an inert gas. Additional nitrogen may be added by means of a separate tank, through the casing or a tube from the surface.
One purpose of the inert gas is to keep the combustion temperature controlled so that it does not become excessive. Thus, the heat is dampened to prevent heat damage to the well casing. The inert gas also helps improve vision through a camera by clearing the smoke caused by the combustion.
A tube may be inserted into the well casing adjacent to the tool to evacuate the fumes, thus also aiding and improving vision through the camera.
In still another embodiment, the nitrogen tank may be eliminated and nitrogen pumped down the well annulus to dampen the combustion temperature and clear the smoke.
Stated in another way, the apparatus of the present invention may be described as one for spraying metal into a desired area of a well casing from the inside of the well casing, the apparatus comprising a steering sub adapted for connection to a tool string, a housing attached to the steering sub such that the steering sub may be used to provide movement of the housing with respect to the tool string, an oxygen tank in the housing wherein the oxygen tank has a quantity of pressurized oxygen therein, an inert gas tank in the housing wherein the inert gas tank has a quantity of pressurized inert gas therein, a fuel tank in the housing wherein the fuel tank has a quantity of fuel therein, a powder container in the housing wherein the powder container has a quantity of metal powder therein and is in communication with the inert gas tank such that the pressurized inert gas tends to push the metal powder out of the powder container, and a spray head connected to the housing and in communication with the oxygen tank, fuel tank and powder container such that fuel, oxygen, inert gas and metal powder are mixed in the spray head and discharged therefrom as a flame spray whereby metal may be deposited on the desired area in the casing.
Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiment is read in conjunction with the drawing which illustrates such embodiment.